1. Field of the Invention
The invention relates generally to radar antenna systems and more particularly, to polarization agile arrays.
2. DESCRIPTION OF THE PRIOR ART
Polarization agile planar arrays are known per se in the radar art. Those prior art devices include stacked slotted waveguides with radiator slots alternately angled on opposite sides of a cross-section plane and appropriate interleaved phase control. An example of such a system is shown in U.S. Pat. No. 3,716,856 entitled "Polarization Adaptive MTI Radar Transponder".
A "Polarization Agile Planar Array" employing dielectrically loaded slotted square coaxial linear arrays in a stacked arrangement with similar interleaved phase control is described in U.S. patent application Ser. No. 861,903, filed Dec. 19, 1977, now U.S. Pat. No. 4,197,541. That application is assigned to the assignee of this application.
The slotted waveguide polarization agile array described in the aforementioned U.S. Pat. No. 3,716,856 involves a relatively expensive array of precisely manufactured waveguide sections having precisely located and dimensioned slotting. The square coaxial line array with slotting in accordance with the aforementioned U.S. patent application Ser. No. 861,903 alleviates many of the problems associated with the slotted waveguide array in that the coaxial linear arrays of which it is composed are not subject to the frequency cut-off limitations inherent in waveguide. Still further, the slotted coaxial sections are relatively easily dielectrically loaded for wave slowing, the resulting structure being considerably lighter and more efficient than the waveguide version. The radiation coupling from the square coaxial array is, however, subject to the expense of cutting slots in the square coaxial walls and although its overall manufacturing cost is substantially less than that of the waveguide device, it nevertheless is substantial.
The present invention is based on certain aspects of the so-called "meander line", and a background understanding of that device is essential to a proper understanding of the present invention. The meander line which borrows from microwave stripline and microstrip technology has been previously referred to as a "sandwich wire antenna". In the year 1957 such an antenna was described by W. Rotman and N. Karas in a paper entitled "The Sandwich Wire Antenna: A New Type of Microwave Line Source Radiator". That paper appeared in the IRE National Conference Record 1957, PT. 1, pp. 162-172. Those authors also describe such devices in an article entitled "The Sandwich Wire Antenna", appearing in the Microwave Journal, Vol. 2, Aug. 1959. A more recent reference appeared in the IEEE Transactions-Antenna and Propagation, Vol. AP 19, No. 5, Sept. 1971, under the title "A New Analysis of the Sandwich Wire Antenna".
The manner in which the present invention exploits the characteristics of the meander line in a new combination having distinct advantages over prior art arrangements for the general purpose, will be understood as this description proceeds.